Top breaking strength is one of the important evaluation indexes, which directly reflects the durability index of knitted fabric when it is deformed and broken by external pressure.

The commonly used test methods of breaking strength are: hydraulic method, air pressure method, steel ball method

1. hydraulic method:

The test principle of hydraulic method is: clamping a certain area of sample on an extensible diaphragm, and applying liquid pressure below the diaphragm.  The volume of the liquid is then increased at a constant rate to expand the diaphragm and the specimen until the specimen ruptures, and the bursting strength and bursting dilation are measured.  Commonly used hydraulic top breaking strength machine MullenC Mullen A top breaking strength machine, the two top breaking machine is the use of glycerin liquid pressure, through the elastic film to produce the top swelling effect to complete the test.  The main difference is that the Mullen C has A range of 2 to 200PSI, while the Mullen A has A range of 10 to 500PSI.  However, when used, it can only be tested to 15%-75% of the full range, otherwise it is easy to burst the elastic film.  For some high elastic fabrics, the customer requires top breakage. If the fabric does not break on Mullen C, it needs to be taken to Mullen A for top breakage.  Mullen hydraulic top breaking strength machine commonly used standard methods are American standard and European standard.  ASTMD3786, whose unit is PSI;  European standard iso13938-1, its unit is KPa.

2.air pressure method:

The test principle of hydraulic pressure method is: the specimen is clamped on an extensible diaphragm, and gas pressure is applied below the diaphragm.  Then, the volume of the gas is increased at a constant speed to expand the diaphragm and the specimen until the specimen ruptures, and the bursting strength and expansion degree are measured.  The commonly used pneumatic fabric bursting strength meter is Truburst, which uses air pump to provide gas pressure, through the elastic film swelling to burst the fabric.  It is composed of an air pump, a tester and a printer. The tester includes a test cup, an elastic film safety cover and so on.  There are two common test cups.  The large cup, which has an area of 50 square centimeters, has an allowable displacement of 70.50 mm and a test time of 20±5 seconds;  Small cup, its area is 7.3 square centimeters, its allowable displacement is 22.50 mm;  The test time was also 20±5 seconds.  There are many standard methods of measuring fabric bursting strength in Truburst, but the most commonly used method is ASTMD 3786, in PSI;  European standard ISO 13938-2, unit is KPa.

3. steel ball method:

The testing principle of the steel ball method is: the sample of a certain area is clamped in the fixed base of the ring sample, the round spherical push rod at a constant moving speed vertically against the sample, so that the sample deformation until the rupture, measured breaking strength.

The commonly used steel ball fabric strength instrument is Instron marble type electronic fabric strength machine.  It uses a steel sphere to cover the fabric.  In this test, we use the American standard.  For example, ASTMD 3787 and ASTMD 6797, both of which are measured in pounds (LBF), have a top breaking speed of 12 inch/min and a ball top rod diameter of 25 mm.  But in the NATIONAL standard, we use the top breaking speed is 100mm/min, the unit is Newton (N), the diameter of the steel ball push rod is 20mm.  Multifunctional pinball electronic fabric strong Instron sampling requirements, the sampling machine to take an area greater than or equal to 100 square centimeters of circular sample five, the sample should be representative, the test area should avoid folding, folding, and avoid the edge of the cloth, the best extension of the diagonal sampling.

4.factors affecting the fabric breaking strength:

1, the internal cause of the fabric itself

The influence of breaking strength and breaking elongation of yarn, when the breaking strength and elongation of yarn in the fabric is large, the top breaking strength of the fabric is high.  The influence of fabric thickness, other things being equal, when the fabric is thick, the top breaking strength is large.  The warp or weft density of a fabric.  When other conditions are the same, the fabric warp and weft density is not at the same time, the fabric must crack along the direction of small density, the crack is linear, the fabric breaking strength is low.  The hook strength of yarn.  In knitted fabrics, when the yarn hook strength is high, the fabric breaking strength is high.  Yarn fineness and coil density also affect the top breaking strength of knitted fabric.  With the increase of yarn density and coil density, the top breaking strength is also increased.  Fabrics in boiling bleaching, hair grinding, dyeing, enzyme washing, resin qualitative finishing and other treatment.  Under the influence of these different processes, the fabric breaking strength decreases, and the use of different processes, different materials, the top breaking strength decline degree is not identic-like.  Generally speaking, the fabric of dark color is lower than that of light color.

2, the influence of external factors

1) The impact of the test method

Using different test methods, test results will also be affected.  Generally speaking, the top breaking strength measured by the hydraulic and pneumatic methods is much more stable than that measured by the steel ball method.  If no special requirements, use hydraulic or pneumatic method.  When the breaking strength is less than 80KPa, there is little difference between the pneumatic method and the hydraulic method, but when the breaking strength カ is greater than 80KPa, the hydraulic method is generally more stable.  Using the same test method, the test range is not the same, the test results will be biased.  Practice has proved that the same hydraulic method, using different range, the test results also have a certain deviation, generally speaking, using small range, the test results will be more accurate.  Therefore, if a small range can be used, the tester should use a small range.

2) Impact of test environment

The testing environment has a great influence on the fabric's breaking strength, so the tester needs to select the corresponding testing environment strictly according to the standard.

3) Influence of operator

Effects of tester readings.  Relative to the hydraulic top breaking strength machine, because different people's eyes are not consistent, or there is no positive reading in the counter, the reading will also have deviation.  The influence of testers choosing the wrong standard method.  Especially compared with the pneumatic fabric bursting strength meter, if the wrong standard method or the wrong test cup, or the wrong calibration, the test results will be greatly affected.  Impact of irregularities in tester operation.  Especially in the test process of hydraulic top breaking strength machine, if the tester can not move the valve handle back to the original position in time in the fabric top breaking moment, the top breaking strength will be large.  The effect of tester sampling.  Each sample must not only be representative, but also be sampled within a specified range. If the tester samples on the edge of the cloth or at a stretched area, the top breaking strength is usually less.

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